clojure.core's unchecked-* (and +/-/*/inc/dec under *unchecked-math*) are long
ops that WRAP on overflow; jolt's checked arithmetic is arbitrary-precision and
its unchecked-* were plain non-wrapping (+ x y), diverging from the JVM. Now they
truncate to the low 64 bits as a signed long, matching Clojure:
(unchecked-add 9223372036854775807 1) => -9223372036854775808
(unchecked-multiply 9223372036854775807 …) => 1
- host/chez/seq.ss: jolt-wrap64 + binary jolt-unc{add,sub,mul,inc,dec,neg}2 and
the variadic clojure.core/unchecked-* fns (def-var!'d in natives-seq.ss, where
def-var! is bound). The overlay's plain unchecked-* defns are removed.
- backend lng-ops: unchecked-+/-/* emit the wrapping jolt-unc* helpers (the
raising fx ops can't wrap on Chez's 61-bit fixnums); unchecked-inc/dec too.
- *unchecked-math* is honored: the analyzer reads it (jolt.host/unchecked-math?)
and rewrites +/-/*/inc/dec to their unchecked-* for the rest of a file that
(set!)s it, like the JVM.
- jolt->fx: a ^long value that overflows the 61-bit fixnum range passes through
as an exact integer instead of erroring (a full-width long from wrapping math).
Also adds Long/bitCount / numberOfLeadingZeros / reverse and Math/getExponent /
scalb (test.check's splittable PRNG uses them).
This lets clojure.test.check load and run quick-check on jolt. re-mint (analyzer/
backend/overlay are seed sources). make test green (+6 corpus rows, 0 new
divergences, numeric gate updated), shakesmoke byte-identical.
A loop var with an integer-literal init now types :long (fx ops) when every recur
arg in its slot is an increment-style step — the var unchanged, inc/dec, or (+/-
var <int-literal>). So (loop [i 0] (recur (inc i))) gets fx1+/fx<? without a hint,
matching how Clojure treats a primitive-long loop counter.
Soundness: only increment steps qualify. A multiplicative or large-growth
accumulator like (recur (* acc 2)) is never seeded, so it stays generic and keeps
arbitrary precision — a bignum-producing loop (e.g. a factorial) is unaffected.
counter-step? gates this; the existing fixpoint demotes anything inconsistent.
test/chez/numeric-test.ss 44/44 (incl. a factorial loop staying bignum-exact while
its counter is fx); full make test green, 0 new corpus divergences.
A ^double/^long return hint on a fn's name now (a) coerces the fn's value on the
way out — exact->inexact / jolt->fx, like a JVM primitive return — and (b) types a
call to it, so an accumulator over the result specializes:
(defn ^double work [^double x ^double y] (+ (* x x) (* y y)))
(loop [acc 0.0] (recur (+ acc (work a b)))) ; (+ acc (work ..)) -> fl+
The analyzer pushes the name's numeric tag onto each arity (:ret-nhint) for the
back-end coercion, and resolve-global surfaces the callee's declared return
(:num-ret, read from var meta) onto the :var node so jolt.passes.numeric types the
call. defn carries the name hint through.
This unblocks the accumulator-over-fn-result pattern that round 2 had to demote.
The win is bounded by call overhead in an open/dispatched build (~1.15x on a hot
loop whose body is a helper call); it compounds with direct-linking and, later,
inlining. A numeric return hint is a contract, like ^long — redefining the var to
return another type in an open build breaks it.
Not yet: per-arity arglist return hints, (defn f (^double [x] ..)). Gate:
test/chez/numeric-test.ss 39/39; full make test green, 0 new corpus divergences.
loop-kinds only typed :double accumulators; a ^long-seeded loop var (e.g.
(loop [acc start] ...) with a ^long start) stayed generic even though it's sound
to fx-type — :long only ever comes from an explicit hint, and a ^long value is
already coerced to a fixnum at fn entry. Keep the init's kind (:double or :long)
through the fixpoint, demoting only on a recur-arg mismatch.
Integer-literal-init loop vars (a bare (loop [i 0] ...)) still stay generic by
design: :long is never seeded from a literal, so a bignum-producing loop keeps
arbitrary precision.
A loop binding whose init is double and whose every recur arg stays double (a
bounded monotone fixpoint) is typed :double, so its arithmetic — and the recur
args feeding it — emit fl-ops. Chez can then keep the accumulator unboxed in a
float register across the loop.
Integer loop vars stay untyped: a bare integer init never seeds :long (same rule
as round 1), so a bignum-producing loop keeps arbitrary precision rather than
overflowing a fixnum. recur-kinds walks only tail position (if/do-ret/let-body),
stopping at nested loop/fn so a loop sees only its own recur.
A/B on a loop-carried double accumulator: 735ms generic -> 500ms typed (1.47x),
closing the gap to the JVM from ~3.3x to ~2.2x. The integer counter stays generic,
which is most of the residual.
A ^double/^long param hint (or a float literal) now drives Chez flonum/fixnum
ops instead of generic arithmetic — JVM-style primitive hints, available in every
build and at -e (not gated on direct-linking or whole-program inference).
New pass jolt.passes.numeric: a local forward type-flow seeded from ^double/^long
fn-param hints (analyzer attaches :nhints per arity) and float literals,
propagated through let inits / arithmetic / if / do. It tags an arithmetic invoke
:num-kind :double|:long when every operand is that kind (an integer literal is a
wildcard, coerced to a flonum in a double op). The back end lowers a tagged node
to fl+/fl-/fl*/fl//fl<?/... or fx+/fx*/fx1+/fxquotient/... (unchecked-add etc.
join the fixnum path; == too). Runs last in run-passes, both branches.
Soundness: :long is seeded ONLY from an explicit ^long hint, never a bare integer
literal, so un-hinted integer code keeps jolt's arbitrary-precision numbers — no
fixnum-overflow surprise, no corpus divergence. :double comes from ^double hints
and float literals (flonum arithmetic is always flonum, matching the generic
result). A ^long hint is a promise the value is a fixnum: fx+ raises on overflow,
like a JVM fixed-width long.
Numeric-hinted params coerce at fn entry (exact->inexact / jolt->fx), the way the
JVM coerces a primitive parameter — so the body's fl*/fx* ops can rely on the
type even when a caller passes an exact int (e.g. Chez's (* 0 1.0) => exact 0).
Round 1 specializes hinted straight-line / fn-body arithmetic. fl-ops are ~4x
generic in a tight Chez loop, but realizing that on loop-carried accumulators
needs loop-var typing — round 2. Sound foundation, gated by test/chez/numeric-test.ss.
